This invention relates to polymer matrixes with fluorescent yellow dye blends therein and that can be formed into films suitable for use in retroreflective sheeting.
It is commonly known that fluorescent colors provide increased visibility for visual signaling under most lighting conditions, but particularly under low natural lighting conditions. These low natural lighting conditions occur at dusk and also at sunrise and present a challenge for traffic sign manufacturers, as well as manufacturers of other highway safety visual signaling articles, such as reflectors, road markers, and the like. If increased visibility of such an article is desired, the article can be colored with fluorescent colorants. Fluorescent colors allow enhanced visibility because the visual contrast that the fluorescent colors create with the environment makes the materials more conspicuous than ordinary non-fluorescent articles. For example, fluorescent colored traffic signs can be effective at increasing the visibility of the signs which increases motorist safety.
Even though fluorescent signs increase motorist safety, their use for yellow signs has been limited due to the difficulty to obtain a true fluorescent yellow. To date, fluorescent colorants are available in only a limited range of hues. For example, fluorescent colorants are commercially available and include fluorescent red, fluorescent orange and fluorescent yellow-green. However, a true fluorescent yellow which meets the chromaticity requirements of Commission Internationale de l""eclairage (CIE) and ASTM is not readily available. As is known in the art, the CIE provides international recommendations for surface colors for visual signaling.
The art of formulating colors from ordinary colorants is well-developed. For example, it is known that a mixture of a blue colorant with a green colorant will give an aqua or a cyan color. However, the art of formulating colors from fluorescent colorants is not well-defined. U.S. Pat. No. 4,443,226 issued to Rohser describes combining thioindigo and/or derivatives of the red and pink series of thioindigo with specific yellow disperse dyestuffs to obtain a shade of fluorescent orange-red. Avery Dennison W-7514 Fluorescent Orange retroreflective sheeting, originally sold as Stimsonite 6380 Fluorescent Orange retroreflective sheeting, uses a combination of red-shade and orange-shade fluorescent dyes to produce the orange color desired. Fluorescent yellow articles comprising a perylene imide dye and a yellow-green fluorescent dye mixed in a polymer matrix are disclosed in U.S. Pat. Nos. 5,672,643, 5,674,622, 5,754,337, and 5,920,429.
The invention provides fluorescent retroreflective sheeting articles which have a yellow color with chromaticity coordinates within the CIE and ASTM requirements.
The inventive fluorescent yellow retroreflective sheeting articles comprise (a) a polymeric matrix, (b) a fluorescent yellow-green dye selected from the group consisting of thioxanthene dyes and benzothiazene dyes, and (c) a second fluorescent dye selected from the group consisting of thioxanthene dyes and thioxanthone dyes. The dyes are chosen such that the resulting retroreflective sheeting has chromaticity coordinates (x,y) within the area defined by (0.425,0.480), (0.465,0.535), (0.557,0.440), and (0.500,0.410) in terms of the CIE 1931 Standard Colorimetric System and measured using 0/45 geometry and evaluated with CIE Standard Illuminant D65. Such retroreflective sheeting will primarily be used in highway signs, reflective safety garments, road pavement markers, reflective materials for commercial graphics, and the like.
Further, in accordance with the invention, a method of manufacturing fluorescent yellow retroreflective sheeting article comprises the steps of: (a) combining a fluorescent yellow-green dye selected from the group consisting of thioxanthene dyes and benzothiazene dyes, and a second fluorescent dye selected from the group consisting of thioxanthene dyes and thioxanthone dyes in a polymeric matrix to form a solid solution and (b) extruding the combination to form a film having chromaticity coordinates (x,y) within the area defined by (0.425,0.480), (0.465,0.535), (0.557,0.440), and (0.500,0.410) in terms of the CIE 1931 Standard Colormetric System and measured using 0/45 geometry and evaluated with CIE Standard Illuminant D65. Such a film will ultimately be incorporated into any of the well known glass-beaded or microprismatic cube corner retroreflective sheeting structures, as is known in the art.